1. Field of the Invention
The present invention relates generally to high-energy radiation survey equipment.
2. Description of the Prior Art and Related Information
Extensive radiation surveys for operational or maintenance purposes are frequently required in the nuclear industry and other industries using radioactive materials. Typically, these surveys are conducted by health physics personnel who place hand-held radiation detectors next to suspected radiation sources or pre-determined radiation survey points. The results of these surveys are then usually manually recorded on printed sketches of the areas surveyed.
This technique suffers from a number of drawbacks. The most significant drawback is the health risk created by the occupational radiation exposure experienced by survey personnel. Another drawback is the variable quality of surveys taken by this technique, which depends on such factors as the placement and orientation of the hand-held detector, the experience and attentiveness of the technician, the quality of the sketch used to document the survey, and the interpretation by the person reviewing the survey data. If the survey or its interpretation do not lead to an accurate understanding of the radiation hazards in the surveyed area, other workers may be exposed to unnecessarily high radiation doses in the future. Other work inefficiencies, leading to increased costs, can also result.
Mechanizing the radiation survey process would reduce the health risk to human workers. To also increase dependability, however, the mechanized survey system must be able to make accurate measurements of relevant variables and provide enough additional information about the surveyed area to facilitate an objective interpretation of survey data. Since efficiency is also a concern, the system should be easily transportable and should be able to adapt to different circumstances in any one location.
The problems to be overcome in meeting these goals can be subtle. For example, the contents of a room to be surveyed may change from day to day. Consequently, the system should not rely on pre-determined knowledge of the room's geometry or contents. In addition, an intervening object may prevent a radiation source from being visible from all points of view in a room. Consequently, a system that takes measurements from pre-determined points in a room, or that may be affected in an unknown way by a radiation source outside the system's field of view, may lack the necessary accuracy and dependability.
Since the purpose of surveys often is identification of radiation health hazards, the system should be able to provide certain types of information that permit the calculation of radiation dose equivalents, which relate to the health effects of radiation. To allow this, the system must be able to measure the energy of the incoming radiation. Additionally, the system should be able to resolve individual sources of radiation and measure the distances from such sources to the detector. To make these measurements more meaningful, the system should provide the human operator with a quick way to identify these sources.
Another problem to be overcome arises from the ability of certain types of high-energy radiation to penetrate, to a greater or lesser degree, the material surrounding a detector. In order to pinpoint a radiation source, the system should be able to detect the radiation coming in from a well-defined direction, while shielding the detector from radiation coming in from all other directions. In the case of gamma radiation, as well as other types of radiation that may be of interest, significant variations in the thickness of the shield will lead to significant variations in the attenuation of the radiation. Such variable attenuation creates difficulties in distinguishing the desired signal (namely, radiation measured along the desired direction) from background noise. Consequently, it is important to achieve substantially uniform attenuation of incident radiation in all directions other than the direction of observation. At the same time, it is necessary to prevent the shielding material from making the device so heavy or bulky that it is no longer easily mobile.
In light of the foregoing, there is a present need for a dependable and accurate radiation survey system.